Just started this playthrough at level 54. I've done the first 2 or 3 missions and now I feel like it's almost impossible. Enemies are level 55 and 56 quite often and absolutely destroy me with just a couple shots.
Need some advice on where/how to gain levels at this point. I do have pretty good gear.

Slag. Make sure you always have something that slags, and just be careful. Ran through pretty much the entire game with two of us, both had slagged skills and guns. It is tough though we died a lot.

What class are you? usually posting class we can give better advice, like gunzerker, your offhand should be the grog nozzelr or rubi.. main hand should be the DPUH... every few levels go farm tokens on Tvhm to upgrade the DPUH n u will rape everything till 72.. and then some.. DPUH/ Grog rapes pretty much anyone

i did really understand much of that..

Do you have all the DLC's?

What character do you play?

If not gunzerker reroll a gunzerker (jk)

Slag item and look up videos for how to get the sandhawk. And like said before get a slag ofc.
Did you use golden keys?

Level in Tvhm to 55 or find a other misson in Uvhm i did enter the Uvhm at lvl 50 and do the story main was to easy after that find a dlc and play to 61 it is hard in uvhm but whn you at 60 you will be fine

i was 58 in mr tourg Dlc was freaky hard went down so many times